December before last, it was snowy and rainy in the rural west of Ireland. John Michael McDonagh, older brother of playwright Martin, was visiting family and out cycling, having had his directorial debut accepted by the Sundance Film Festival and wondering what was to become of his film, The Guard. After a few hundred lonely yards he came upon the body of dead cat, so he got off his bike and dragged it to the side of the road. Further along, there was another body, this one much bigger, about three or four feet long. What the hell was it?

He soon found out. It was, he recalls, "a fucking badger!" So once again he thought he'd do the right thing, be nice about it. "Have you ever lifted up a badger?" he asks. "They're really heavy! And here I was, carrying this badger carcass. And I'm thinking, 'But I'm an auteur! Would Lars von Trier be carrying a badger?! Is this gonna be my life – cycling round, picking up roadkill?'"

Luckily for McDonagh, The Guard was nothing but successful: not bad for a wicked comedy about a sexist, racist, even perhaps educationally subnormal garda who takes on a trio of drug-smugglers single-handed. The Sundance lot loved it, the Irish made it their biggest independently funded film of all time, and the Hollywood Foreign Press Association, an outfit feebly drawn to A-list celebrities, redeemed itself by nominating its star, Brendan Gleeson, for a Golden Globe. It's still playing in the US, after 23 weeks.

"I thought the film would be popular," says the deadpan McDonagh, 44 this year, "because it was kinda funny. But I did wonder how it would be received in Ireland, because of the way a lot of Irish journalists have this overweening … er, let's say they're really insecure about how Ireland is perceived by the rest of the world, which Irish people themselves aren't really bothered about that much. So I thought they might come after me, for being a London-Irish writer director making fun of the people out in the west of Ireland – which, if you see the film, really isn't true …

"But, y'know, I thought it would do better in the UK, to be honest. We were told Irish films don't usually play well in the UK, which is a bit of a self-fulfilling prophecy. But it is a bit odd when your film does better in Germany … "

McDonagh, however, was most pleased to see the film not only taking out his brother Martin's black comedy In Bruges in their parents' homeland, but also Ken Loach's political drama The Wind That Shakes The Barley to become the biggest Irish indie film ever.

"We just beat him in the last few weeks, by a couple of hundred euros or whatever. I like to say that Ken had about 30 goes at it. But I've only had one."

As text, it's hard to appreciate McDonagh's dry, sardonic humour. Despite his apparent glee at beating his brother's film, he claims there was never any real rivalry. "Well, not when he was writing his plays," he laughs, "because I don't like the theatre. I was happy for him when he won the Oscar for Six-Shooter, his short film. But I guess it started when he got In Bruges set up – even before it was shot – that I was getting a bit, er, testy, let's say, and the old ulcer was forming. But once I made The Guard, and it did quite well, all that's gone away now."

'People say it's nice to get nominated, you should applaud the winner … But I have none of those feelings, I just stew'

John Michael McDonagh Photograph: Andrew H Walker/Getty

Which is just as well. McDonagh has often said that The Guard was a film written in frustration, born of (as he says) "rage, bitterness and contempt" after his intended debut was scuppered by a star he says "couldn't fucking act". Is it easy to use that same fuel, now the film has been embraced with such affection?

"I know, I know," he laughs, "but I still try to grab any kind of bitterness I can, anywhere I can find it. As you may know from my reaction at losing at the British Independent Film Awards, I respond to everything with appallingly bad grace. So anywhere I can find it, I hoard it. I'm not sure about those events. People always say, 'Well, you should take it in good part, it's nice to get nominated, you should applaud the winner … ' But I have none of those feelings! I just stew."

The Guardian asks if he ever felt like giving up. "Yes, psychologically," he admits. "But in reality there was nothing else I could do, apart from writing. I had no other skills. So I couldn't really give up, I just had to keep persevering. You can pick up money here and there. It's not a great living but it's enough to survive on."

We'll gloss over his experience as screenwriter on the Heath Ledger vehicle Ned Kelly, which McDonagh savagely dissed from the stage when The Guard opened last year's Edinburgh Film Festival ("If you've been complaining about the way you've been treated for so many years in private, it's a bit cowardly not to say it in public," he reasons). So surely this apparently misanthropic individual would struggle in the US? Not so, it seems. "Generally speaking, most people in the film industry have seen The Guard," he says. "Especially in America. I went over to do a week of meetings recently, and I thought I'd only have three or four, and I could sit by the pool. But there were about 18, cos they really do like to chase success. Owen Wilson wanted to meet me. I thought it would just be half an hour – I ended up drinking with him for about four hours in a hotel in Santa Monica. If they like your work, they're actually really inclusive over there."

And from the UK? "Nothing at all! Two things came in from the UK – both of them interesting, but not up my alley – and that was it. No other interest, nobody wanting to meet!" He laughs, softly and without rancour: "What does that tell you? I think it tells you that there's not a lot going on in the British film industry."

'I said with all these Catholic abuse scandals we should write a film about a good priest where everyone else is bad'

Don Cheadle and Brendan Gleeson . Photograph: Allstar

Still, McDonagh will, fingers crossed, be making his second movie later this year, a drama called Calvary. There will, he promises, be some dark humour in it, but overall it will be much more dramatic. "Y'know," he says, "I naively thought that, with the success of The Guard, people would be throwing money at me, as long as I got a decent cast. But it actually does all come down to the material; people will only give you what they think it will be worth, for them to recoup."

Shot out in the west of Ireland again, the film is to reteam McDonagh with Gleeson, this time starring as a more clear-cut hero, or rather a good priest who's tormented by the people in his community. "Brendan and I were in a lock-in in a pub in Spiddal," McDonagh recalls, "and towards the end of the night I said, 'I bet with all the scandals in the Catholic church, a lot of crappy Irish film-makers are going to be making really heavy, depressing films about abusive priests.' I said, 'We should do the exact opposite: write a film about a good priest where everyone else is bad.' And Brendan drunkenly said, 'I've always wanted to play a good priest.' So it started from there."

And what else can we expect? Thinking back to The Guard's defeat at the Bifas, where it lost to Paddy Considine's hard-hitting, social-realist Tyrannosaur, McDonagh has a brainwave. "Paddy Considine, he kills a dog in his movie and he's won all these awards. One of them's a pitbull. Right? Well, I'm gonna kill a golden Labrador. I'm gonna push the envelope. And if I can get Brendan Gleeson to piss on it, I might end up in Sight & Sound's top 10 of the year."